The primary thrust of the Project is to investigate mechanisms concerned with regulation of testicular function in general. Most of the fundamental studies are directed towards questions which may be of relevance to work dealing with the development of a male contraceptive. Applied studies will deal directly with investigation of the feasibility of using hormonal preparations for male contraception and with problems related to diagnosis and treatment of testicular disorders. In order to make this approach scientifically valid and clinically safe a body of fundamental knowledge concerned specifically with mechanisms involved in regulation of gonadotropin synthesis and release by the gonadal steroids, with the role of gonadotropins and steroids in spermatogenesis and with the biochemical mechanisms of gonadotropin, testosterone, and estrogen action needs to be accumulated. The fundamental studies proposed in this application will be directed towards acquisition of this knowledge and elucidation of these mechanisms. In addition, studies dealing with kinetics of population growth and the role of androgens in it from physiologic and behavioral viewpoint will be conducted. These studies should place our entire research effort in a broader perspective through an inquiry into the models of natural mechanisms of population control operating in lower species.